Every country and continent has an adjective that can be used to describe people and things from that place. Those same adjectives can also be used as nouns to refer to people from that place.
|American (North + South)||americano*|
|American from USA||estadounidense|
Many nationalities are identical to their respective languages.
Nationalities, which are both adjectives and proper nouns, are not capitalized in Spanish. When feminine and/or plural, they follow the same agreement rules as other adjectives.
* This refers to anyone from either North or South America; to talk about someone from the United States, use estadounidense.